CPI-based monomers have been the subject of recent publications. For instance, the compounds (+)-CC-1065 and the duocarmycins are natural products isolated from the culture broth of Streptomyces species, which have been shown to exert ultrapotent activity against cultured cancer cells and in experimental animals. (+)-Yatakemycin has been isolated from Streptomyces sp. and represents the most potent member of this class of natural products. The biological activity of these natural products is believed to be related to a characteristic sequence-selective DNA alkylation of adenine N3 in AT-rich sites by the least substituted carbon of the activated cyclopropane. This minor groove binding is thought to initiate a cascade of cellular events leading to apoptosis as observed for the duocarmycins (“Chemical and Biological Explorations of the Family of CC-1065 and the Duocarmycin Natural Products”, Current Topics in Medicinal Chemistry, 2009, 9, 1494-1524). The key structural motif in these and related analogs is the CPI structures which is the reactive group that alkylates DNA:

The CPI prodrug form converts to the active drug species in the biological medium by an intramolecular cyclization reaction. (The term “CPI” is derived from the chemical name: 1,2,8,8a-tetrahydrocyclopropa[c]pyrrolo[3,2-e]indol-4(5H)-one.) The CPI prodrug thus converts to an active drug species by an intramolecular cyclization reaction. The phenol synthetic precursors (prodrug form) possess indistinguishable biological properties (DNA alkylation efficiency and selectivity, in vitro cytotoxic activity, in vivo antitumor activity) in comparison to the cyclopropane derivatives themselves (active form) (“Design, Synthesis, and Evaluation of Duocarmycin O-Amino Phenol Prodrugs Subject to Tunable Reductive Activation”, J. Med. Chem. 2010, 53, 7731-7738). In other words, it does not matter whether the CPI warhead is in its active cyclopropanated form or in its prodrug form. Important to note is that in these compounds only one CPI motif is present, hence these compounds act as DNA mono-alkylators. Several other synthetic analogs of the CPI structures have subsequently been developed, i.e. those shown in (“Chemical and Biological Explorations of the Family of CC-1065 and the Duocarmycin Natural Products”, Current Topics in Medicinal Chemistry, 2009, 9, 1494-1524). Of note in this reference are the synthetic analogs CBI, CpzI, CFI, CI and CBQ. Mono-alkylating duocramycin analogs have been extensively studied in preclinical and clinical studies (“Chemical and Biological Explorations of the Family of CC-1065 and the Duocarmycin Natural Products”, Current Topics in Medicinal Chemistry, 2009, 9, 1494-1524).
A separate but related class of compounds are bifunctional analogs that contain two active DNA alkylation motifs (i.e. a CPI). These compounds are different to the conventional duocarmyins in that they lack the moiety within duocarmycins, which functions as the DNA recognition motifs. Instead, these bifunctional compounds simply contain two alkylation (i.e. two CPI motifs) fused together. Due to the presence of two reactive alkylation motifs these compounds are active DNA cross linkers, whereas compounds with only one alkylation motif (all duocarmycins) are only DNA mono-alkylators.

The compounds shown above are representative examples from the literature and are reported to be potent cytotoxins: A (“Glycosidic Prodrugs of Highly Potent Bifunctional Duocarmycin Derivatives for Selective Treatment of Cancer”, Angew. Chem. Int. Ed. 2010, 49, 7336-7339; “Duocarmycin Analogues Target Aldehyde Dehydrogenase 1 in Lung Cancer Cells”, Angew. Chem. Int. Ed. 2012, 51, 2874-2877; “Bifunctional prodrugs and drugs”, WO 2011/054837, DE 10 2009 051 799; “The Two Faces of Potent Antitumor Duocarmycin-Based Drugs: A Structural Dissection Reveals Disparate Motifs for DNA versus Aldehyde Dehydrogenase 1 Affinity”, Angew. Chem. Int. Ed. 2013, 52, 1-6. B (“Interstrand DNA Cross-linking with Dimers of the Spirocyclopropyl Alkylating Moiety of CC-1065”, J. Am. Chem. SOC. 1989, 11 1, 6428-6429; “CC-1065 analogs having two CPI subunits useful as antitumor agents and ultraviolet light absorbers”, Eur. Pat. Appl. (1990), EP 359454, also for compounds C and D; C (“Synthesis and DNA Cross-Linking by a Rigid CPI Dimer”, J. Am. Chem. SOC. 1991, 113, 8994-8995; “Nucleotide Preferences for DNA Interstrand Cross-Linking Induced by the Cyclopropylpyrroloindole Analogue U-77,779”, Biochemistry 1993, 32, 2592-2600; “Determination of the Structural Role of the Internal Guanine-Cytosine Base Pair in Recognition of a Seven-Base-Pair Sequence Cross-Linked by Bizelesin”, Biochemistry 1995, 34, 11005-11016; “Analysis of the Monoalkylation and Cross-Linking Sequence Specificity of Bizelesin, a Bifunctional Alkylation Agent Related to (+)-CC-1065”, J. Am. Chem. SOC. 1993, 115, 5925-5933; “Mapping of DNA Alkylation Sites Induced by Adozelesin and Bizelesin in Human Cells by Ligation-Mediated Polymerase Chain Reaction”, Biochemistry 1994, 33, 6024-6030; “DNA Interstrand Cross-Links Induced by the Cyclopropylpyrroloindole Antitumor Agent Bizelesin Are Reversible upon Exposure to Alkali”, Biochemistry 1993, 32, 9108-9114; “Replacement of the Bizelesin Ureadiyl Linkage by a Guanidinium Moiety Retards Translocation from Monoalkylation to Cross-Linking Sites on DNA”, J. Am. Chem. Soc. 1997, 119, 3434-3442; “DNA interstrand cross-linking, DNA sequence specificity, and induced conformational changes produced by a dimeric analog of (+)-CC-1065”, Anti-Cancer Drug Design (1991), 6, 427-452; “A phase I study of bizelesin, a highly potent and selective DNA interactive agent, in patients with advanced solid malignancies”, Ann Oncol. 2003 May; 14(5):775-782; “A Phase I study of bizelesin (NSC 615291) in patients with advanced solid tumors”, Clin Cancer Res. 2002, 3, 712-717; “Solution conformation of a bizelesin A-tract duplex adduct: DNA-DNA cross-linking of an A-tract straightens out bent DNA”, J Mol Biol. 1995, 252, 86-101; “Preclinical pharmacology of bizelesin, a potent bifunctional analog of the DNA-binding antibiotic CC-1065”, Cancer Chemother Pharmacol. 1994, 34, 317-322. D (“CC-1065 analogs having two CPI subunits useful as antitumor agents and ultraviolet light absorbers”, Eur. Pat. Appl. (1990), EP 359454. The active DNA alkylation motif can in principle exist in either a prodrug form that converts to the active drug in the biological medium, or in its active state which does not require further conversion. The prodrug-to-active drug conversion for the bifunctional cross linkers is exemplified with the CBI dimer shown below:

The same conversion takes place for all bifunctional cross linkers that exist in their prodrug states. Other related bifunctional cross linkers have been reported. (“Chemical and Biological Explorations of the Family of CC-1065 and the Duocarmycin Natural Products”, Current Topics in Medicinal Chemistry, 2009, 9, 1494-1524; “DNA interstrand cross-linking agents and their chemotherapeutic potential”, Curr Med Chem. 2012, 19, 364-385; “Design and Synthesis of a Novel DNA-DNA Interstrand Adenine-Guanine Cross-Linking Agent”, J. Am. Chem. Soc. 2001, 123, 4865-4866; “Effect of base sequence on the DNA cross-linking properties of pyrrolobenzodiazepine (PBD) dimers”, Nucleic Acids Res. 2011, 39, 5800-5812; “Sequence-selective recognition of duplex DNA through covalent interstrand cross-linking: kinetic and molecular modeling studies with pyrrolobenzodiazepine dimers”, Biochemistry. 2003, 42, 8232-8239; “Bifunctional alkylating agents derived from duocarmycin SA: potent antitumor activity with altered sequence selectivity”, Bioorg Med Chem Lett. 2000, 10, 495-498; “Design, Synthesis and Cytotoxicity Evaluation of 1-Chloromethyl-5-hydroxy-1,2-dihydro-3H-benz[e]indole (seco-CBI) Dimers”, Bioorganic & Medicinal Chemistry 2000, 8, 1607-1617.
A phosphate pro-drug strategy for monomeric seco-CBI containing cytotoxins has been described by Zhao et al. (“Synthesis and biological evaluation of antibody conjugates of phosphate prodrugs of cytotoxic DNA alkylators for the targeted treatment of cancer”, J. Med. Chem. 2012, 55, 766-782) and Zhang et al. (“Immunoconjugates containing phosphate-prodrugged DNA minor groove binding agents, compositions containing them, and methods of making them and their use for treating cancer”, WO 2012/162482).
None of the above-mentioned compounds, which have two CBI and/or CPI cores linked together to form a dimeric species (so called CBI dimers, CPI dimers, or CBI/CPI dimers), have been considered for use in an antibody drug conjugates (ADCs) as a payload.
Conjugation of drugs to antibodies, either directly or via linkers, involves a consideration of a variety of factors, including the identity and location of the chemical group for conjugation of the drug, the mechanism of drug release, the structural elements providing drug release, and the structural modification to the released free drug. In addition, if the drug is to be released after antibody internalization, the mechanism of drug release must be consonant with the intracellular trafficking of the conjugate.
While a number of different drug classes have been tried for delivery by antibodies, only a few drug classes have proved efficacious as antibody drug conjugates while maintaining a suitable toxicity profile. One such class is the auristatins, derivatives of the natural product dolastatin 10. Representative auristatins include (N-methylvaline-valine-dolaisoleuine-dolaproine-norephedrine) and (N-methylvaline-valine-dolaisoleuine-dolaproine-phenylalanine). Other related tubulin binding agents include the maytansines (for instance see “Cell-binding agent-maytansinoid conjugates linked via a noncleavable linker, preparation methods, and methods using them for targeting specific cell populations” published as WO 2005/037992). Other cytotoxic drugs that have been employed in linkage with antibodies include DNA-binding drugs such as calicheamicin that causes sequence-specific double-stranded DNA cleavage. Another class of DNA binding cytotoxic drugs employed in ADCs includes dimeric pyrrolobenzodiazepines (for instance see “Preparation of unsymmetrical pyrrolobenzodiazepines dimers for inclusion in targeted conjugates” published as WO2013/041606). Another such class of drug where antibody delivery has been attempted is DNA binding alkylating agents, such as the duocarmycin analog CC-1065 (see “Preparation of CC-1065 analogs and their conjugates for treatment of cancer” published as WO2010/062171) and related compounds (see “Antibody-drug peptide conjugates for use as cytotoxins in cancer treatment” published as WO 2007/038658, and “Immunoconjugates containing phosphate-prodrugged DNA minor groove binding agents, compositions containing them, and methods of making them and their use for treating cancer” published as WO2012/162482). However, these drugs all have limitations relating to disease indications and treatment profile, and thus there remains a need for additional drugs with improved properties deliverable via antibody conjugation. Accordingly, the present invention provides novel ADCs with dimers as payloads.